Autonomous vehicles, such as vehicles that do not require a human driver, can be used to aid in the transport of passengers or items from one location to another. Such vehicles may operate in a fully autonomous mode where passengers may provide some initial input, such as a pickup or destination location, and the vehicle maneuvers itself to that location.
In order to provide a safe and comfortable trajectory for a self-driving vehicle that operates in an autonomous driving mode or driverless vehicle, it is necessary to determine an appropriate type of reaction to any objects or agents such as other vehicles, bicyclists, pedestrians, etc., in the environment of the vehicle. Typically, there are a finite number of reactions to a given object, such as passing to the left of the object, passing to the right, stopping in front of the object, remaining behind of the object, etc. However, when there are multiple objects, the number of possible reactions can grow exponentially.
For humans, a simple solution to this problem is to “group” certain objects together and respond to those objects as if a singular entity. Humans use multiple cues when deciding to react to the group, based on proximity, object type, relative motion, etc. In addition, humans may recognize that groups of objects sometimes carry semantics that are not necessarily obvious when looking at any given object in isolation. For example, a group of small children accompanied by one or more adults may motivate a different reaction than a single child with an adult, and a line of slow-moving vehicles with flashing lights may be a funeral procession.